GAZA CITY, Palestinian Territories (AFP) ― Israeli warplanes kept up deadly raids on Gaza on Friday but failed to stop Palestinian militants firing rockets across the border, as the United States offered to help negotiate a truce.

As the violence worsened, U.S. President Barack Obama in a phone call to Israeli Prime Minister Benjamin Netanyahu said his government was willing to broker a cease-fire.

Obama said he was concerned the fighting could escalate and “called for all sides to do everything they can to protect the lives of civilians,” the White House said.

U.N. chief Ban Ki-moon also appealed Thursday for an immediate cease-fire at an emergency meeting of the Security Council, saying it was “more urgent than ever” to establish a cease-fire.

A ball of fire is seen following an Israeli air strike on Rafah in the southern Gaza Strip on Friday. ( AFP-Yonhap)

Russian President Vladimir Putin issued a similar plea in a phone call to Netanyahu, urging an immediate end to the bloodshed and expressing concern over civilian casualties.

But Israel appeared bent on dealing a fatal blow to the Islamist movement Hamas which controls Gaza, with Netanyahu reportedly saying talk of a cease-fire was “not even on the agenda.”

Israeli air strikes killed more than 30 Palestinians on Thursday alone, many of them women and children.

Hamas, the Palestinian group ruling Gaza, also appeared to have no interest in letting up, striking deep inside Israel over the past 48 hours, with rockets crashing down near Jerusalem and Tel Aviv and even as far away as Hadera, 116 kilometers to the north.

Senior Hamas member and the movement’s former Gaza prime minister Ismail Haniya ruled out any backing down by the Islamist movement.

“The enemy (Israel) is the one that started this aggression and it must stop, because we are (simply) defending ourselves,” Haniya said in a statement early Friday.

Sirens wailed across Jerusalem for the second time running on Thursday and a series of loud explosions echoed across the city as the Iron Dome antimissile system shot down two rockets fired from Gaza, the army said.

Another two crashed down in open areas in the occupied West Bank, one hitting near the Maaleh Adumim settlement and the other landing near Ofer, an Israeli military prison just west of Ramallah, witnesses and security officials said.

Hamas claimed it fired four missiles at Jerusalem.

Since the start of the Israeli campaign in the early hours of Tuesday, some 90 Palestinians have been killed and more than 500 injured, according to Gaza’s emergency services spokesman Ashraf al-Qudra.

As the number of victims in Gaza rose, Egypt opened the Rafah border crossing, with hospitals in north Sinai placed on standby to receive the wounded, Egyptian state news agency MENA said.

“We are still facing a difficult, complex and complicated campaign,” Netanyahu said after a security cabinet meeting.

The violence has emptied the streets from Gaza City to Tel Aviv, as both Israelis and Palestinians take shelter indoors for fear of being caught in the open when the next rocket or missile hits.

Israel has confirmed preparations are under way for a possible ground attack, with tanks seen massing along the border and Netanyahu facing mounting pressure from coalition hardliners to put boots back on the ground in the territory from which Israeli troops and settlers withdrew in 2005.

Since the start of the operation, the Israeli military’s biggest offensive on Gaza since November 2012, its forces have hit over 860 “terror sites,” 110 of them on Thursday.

In the same period, Gaza militants fired 490 rockets, of which more than 370 struck Israel, while another 87 rockets were intercepted, an army statement said. Of the total, over 120 struck Israel on Thursday, while another 24 were intercepted.

Neither side has shown any sign of backing down, and Israel has approved the call-up of 40,000 reservists.

Analysts said Hamas had a clear aim: to drag Israel into a ground war hoping to inflict heavy casualties on its troops who would likely come under fire from anti-tank missiles and explosive devices.

Militants would also be seeking to capture Israeli soldiers to use as leverage.

In a news conference, Hamas’ armed wing the Ezzedine al-Qassam Brigades issued a veiled threat to kidnap soldiers, saying a “ground war will be a chance to free Palestinian prisoners.”

Hamas spokesman Sami Abu Zuhri said in a separate statement that Israel would “pay the price for its crimes,” saying an Israeli ground assault would be a mistake, calling Israeli troops “cowards.”